Potentiometers



Jan. 3, 1956 FIQ 2 mum? J. w. KNOLL 2,729,729

POTENTIOMETERS Filed Feb. 29, 1952 lllllilll INVENTOR.

United States Patent POTENTIOMETERS John W. Knoll, Philadelphia, Pa. Application February 29, 1952, Serial No. 274,179

3 Claims. (Cl. 201-56) This invention relates to variable resistance devices and more particularly to certain structural features of such devices as potentiometers, rheostats, and the like.

Potentiometers, rheostats, and the like are provided with a solid shaft on which there is mounted a sliding contact member adapted to make an electrical connection with the resistance element. Upon rotation of the shaft, the sliding contact is moved over or along the resistor whereby the effective resistance of the device is altered. Where the device is to be operated in conjunction with other equipment it is necessary to couple the shaft to the other instruments by the use of gears, belts, couplings, and the like.

The principal purpose of my invention is to provide a variable resistance device with a tubular shaft or stem of relatively large internal diameter.

Another purpose of my invention is to provide a variable resistance device with a tubular shaft or stem adapted to receive adapter bushings having apertures of desired internal diameter adapted to accommodate the diameter of a driving shaft.

Other objects and advantages of this invention will become apparent from the description and claims which follow.

in the drawings:

Fig. l is a perspective view, partly in section, of a potentiometer made in accordance with my invention.

Fig. 2 is a sectional view, partly diagrammatical, of a rheostat made in accordance with this invention.

The potentiometer of Fig. l is provided with a cylindrical case or housing 1 formed of a suitable dielectric material such as a molded synthetic plastic or resin. One end of the housing is provided with an integral end 2 which is provided with an aperture through which the shaft extends. The resistance element may be in the form of a helical winding or coil of resistance wire 3 which is secured to the inner surface of the housing. Terminals 4 are secured to the housing and are connected electrically to the respective ends of the resistance element. It is obvious that in the case of a rheostat, only one end of the resistance element will be connected to a terminal element. A terminal 5 may be secured to the housing, or the housing may be provided with a groove at its open end to receive the terminal 5.

A closure 6 is provided for the open end of the cylindrical housing 1. The closure is provided with a centrally located aperture in alignment with the aperture in the end 2. Bearing members 7 are disposed in the aperture in the end 2 of the housing and in the aperture in the closure 6, being retained therein by retaining rings or nuts 8. Mounting studs 9 are secured to end 2 and closure 6, as by embedding the heads of the studs in the material during molding, and serve as a means for fixedly mounting the device to a suitable support.

A tubular shaft or stem 10 having a relatively large internal diameter is supported rotatably in the bearings 7, extending beyond the bearings at both ends of the housing. A rotor element 11 is secured to the tubular shaft or stem and is provided with a longitudinal groove 12. The length of the rotor element 11 is sufiicient to prevent longitudinal displacement of the tubular shaft or stem. A collector collar or ring 13 is secured to the rotor element 11 adjacent one end thereof. Electrical connection of the collector collar or ring 13 to the external terminal 5 is made by means of brush type contact 14 which may be formed of spring metal. In order to reduce the contact resistance between the collector collar and the brush contact suitable silver alloy contact members 15 may be secured to the brush contact.

The sliding contact assembly comprises slide-block 16 adapted to move along the longitudinal groove 12 in the rotor element. The slide-block is formed of a dielectric material and is provided with outwardly extending fins 17 adapted to straddle the resistance wire. Thus upon rotation of the tubular stem and rotor element the slide-block is moved longitudinally along the groove as the fins track the path of the helical winding. Electrical contact with the resistance element is made by means of a spring metal member 18 secured to the slide-block 16. Electrical contact with the resistance wire may be made by a contact element 19 secured to member 18, such as a. silver alloy element, in order to reduce the contact resistance. The sliding contact may be connected electrically to the collector ring by means of a suitable flexible conductor (not shown).

A series of adapter bushings are provided for the ends of the tubular shaft or stem so as to permit the rotor to be coupled with any desired external shaft. The adapter bushings 20 are preferably provided with a reduced portion 21 of an external diameter to permit the reduced portion to be inserted into the ends of the tubular shaft or stem 10. This diameter may correspond to standard press-fit tolerances so as to form a rigid assembly upon pressing, or the bushings may be secured to the shaft 10 by pins or screws, as desired. The size of the apertures 22 in the bushings will be dependent upon the shaft to which the device is to be coupled. A series of bushings may be provided having apertures varying from 0.0625 inch to about 1 inch in diameter in increments of 0.0625 inch so as to accommodate driving or external shafts of this range. The bushings are provided with a set screw 23 to lock the external shaft to the bushing. Where the device is located between two shafts of different size, each of the bushings is selected to accommodate the respective shaft size and each bushing is provided with a locking screw.

The tubular shaft or stem and adapter bushing construction is equally applicable to the conventional variable resistance devices of the type illustrated in Fig. 2. The rheostat as there shown includes a supporting base 25 which may be of insulation material. A resistor element 26 is supported on the base by any desired means. The resistor element 26 may consist of a support of in sulation material about which is wound a resistance wire, or the element may consist of a ring of a resistor mate rial. One end of the resistor element is connected electrically to a terminal 27. The bearing 28 is secured to the supporting base. The tubular shaft or stem 29 is rotatably mounted in the bearing 28. A movable contactor 30 is fixedly secured to the tubular shaft or stem, the free end making contact with the resistor element 26. Electrical connection between contactor 30 and terminal 31 may be made by means of a conductor 32. An adapter bushing 33 is secured to the end of the tubular shaft or stem 29, as described hereinbefore. If desired, a similar bushing may be secured to the opposite end of the shaft.

The employment of the tubular shaft thus permits coupling to shafts of a wide variety of sizes without supplementary gearing and the like. The tubular shaft also permits the device to be readily installed in combination with other instruments without the necessity of cutting the shafts of the other instruments to which the resistance device is to be coupled.

I claim:

1. A variable resistance device comprising a cylindrical housing, a helical coil of resistance wire mounted internally of said housing, at least one external terminal of said housing, at least one external terminal on said housing connected electrically to one end of said helical coil, a tubular shaft rotatably mounted concentrically in said housing and having at least one end extending from said housing, a contact member mounted on said tubular shaft and adapted to move longitudinally of said tubular shaft, said contact member making electrical contact with said helical coil and adapted to make electrical contact with successive portions of said helical coil vupon rotation of said tubular shaft, a terminal extending exteriorly of said housing and connected electrically with said movable contact, and an adapter bushing in at least one end of said tubular shaft, said bushing having an aperture therein adapted to receive an external shaft.

2. A variable resistance device comprising a cylindrical housing, a helical coil of resistance wire mounted on the inner wall of said housing, at least one external terminal on said housing connected electrically to one end of said helical coil, a tubular shaft rotatably mounted concentrically in said housing and having at least one end extending from said housing, a cylindrical rotor element secured to said tubular shaft within said housing, said rotor element having a longitudinally extending groove therein, a slideblock slidably mounted in said groove, said slide-block being adapted to track said wire and thereby move along said groove upon rotation of said tubular shaft and rotor, a contact member mounted on said slide-block making electrical contact with said wire and adapted to make electrical contact with successive portions of said helical coil upon rotation of said tubular shaft and rotor, a terminal extending exteriorly of said housing and connected electrically to said contact member, and an adapter bushing in at least one end of said tubular shaft, said bushing having an aperture therein adapted to receive an external shaft.

3. A variable resistance device comprising a cylindrical housing having one end closed, said end having an aperture therein, a bearing mounted in said aperture, a helical coil of resistance wire secured to the inner cylindrical wall of said housing, a pair of external terminals on said housing, each of said terminals connected electrically to one end of said helical coil, a closure for the Open end of said housing, said closure having an aperture therein, a bearing mounted in said aperture, a tubular shaft rotatably mounted between said bearings and projecting beyond the ends of said housing, a cylindrical rotor element secured to said tubular shaft between said bearings, said rotor element having a longitudinally extending groove therein, a collector ring secured to said rotor element adjacent one end thereof, a brush contact mounted in said housing and making electrical contact with said collector ring, an external terminal on said housing connected electrically With said brush contact, a slide-block mounted in said groove for slidable movement along said groove, a pair of fins on said block extending between adjacent turns of said helical coil whereby said block is moved along said groove as said fins track said wire upon rotation of said tubular shaft and rotor element, a contact member mounted on said slide-block making electrical contact with said Wire and adapted to make electrical contact with successive portions of said helical coil upon rotation of said tubular shaft and rotor element, said contact member being connected electrically with said collector ring, and an adapter bushing in at least one end of said tubular shaft, said bushing having an aperture therein adapted to receive an external shaft.

References Cited inthe file of this patent UNITED STATES PATENTS 

